A motor-vehicle door latch normally has a housing, a lock fork on the housing engageable with a door bolt and pivotable between a holding position engaged around the bolt and retaining it on the housing and a freeing position permitting the door bolt to move into and out of the housing, and a release pawl engageable with the fork and displaceable between a latched position retaining the fork in the holding position and an unlatched position unengageable with the fork and permitting the fork to move into the freeing position. An actuating mechanism is movable between an actuated position and an unactuated position and normally has an inside and an outside actuating lever connected to respective door handles. A coupling part is displaceable on the housing between a coupling position connecting the actuating mechanism to the release pawl for displacement of the release pawl into the unlatched position on displacement of the actuating mechanism into the actuated position and a decoupling position for disconnecting the actuating mechanism from the release pawl. Thus in the decoupling position operation of the actuating mechanism does not affect the release pawl. A central locking element is displaceable on the housing between locked and unlocked positions and is connected via a locking mechanism normally also operable by at least an inside locking element with the coupling part for displacing the coupling part into the decoupling position on displacement of the central locking element into the locked position and for displacing the coupling part into the coupling position on displacement of the central locking element into the unlocked position.
Thus such a latch, when used on for example on a front vehicle door, is connected to four different things: the inside locking element which typically is a button or small lever, the outside locking element which is normally a key-operated cylinder, and inside and outside latching handles. The latch mechanism can be operated by the inside handle when it is locked and in many systems the inside handle can also be disconnected in the locked position of the latch.
In commonly owned U.S. Pat. No. 4,735,447 the vehicle door latch for use in combination with a door bolt has an outer housing part formed with a recess in which the bolt is receivable and is provided with the latch fork and with a latch pawl pivotal on the outer housing part into and out of a position retaining the fork in the locked position. A middle housing part lying on the outer housing part carries the latching mechanism connected to the pawl for moving same into and out of its position retaining the fork in the locked position. The locking mechanism connected to the latching mechanism prevents same from operating the pawl to latch the fork, and the locking and opening levers respectively connected to the locking and latching mechanisms and connectable respectively to the outside door lock and outside door handle operates the respective mechanisms. An inner housing part lying on the middle housing part carries respective locking and opening links connected to the locking and latching mechanisms for operating same and a servomotor is connected to the locking mechanism for operating same and preventing operation of the latching mechanism by the opening link and lever. Fasteners secure the parts to contain the mechanisms and servomotor.
While such a latch is an excellent system for use on a front vehicle door, it is less suitable for use on a rear door or on a trunk lid. The rear doors are not usually provided with outside locking connections, that is the only way to unlock the rear doors is from inside the vehicle. Thus any connection for an outside lock element is superfluous on a rear-door latch. In addition when such a lock is provided on a trunk lid, where an outside locking cylinder and inside mechanical latching connection are provided, the orientation of the cylinder relative to the lock is frequently greatly different from that used on a front vehicle door. Thus separate locks must be built for the rear doors and trunk lid.